Hermetically sealed electric power terminal feed-throughs provide an airtight electrical feed-through for use in conjunction with hermetically sealed devices where leakage into or from such devices, by way of the feed-throughs, is effectively precluded. For the terminal feed-throughs to function safely and effectively for their intended purpose, the terminal feed-throughs require that their conductor pins be electrically insulated from and hermetically sealed to the body through which they pass and that an optimum air path be established and thereafter maintained between adjacent pins and opposite sides of the body.
Referring to FIG. 1, a typical electrical power terminal feed-through 10 for a fractional compressor application is shown to be installed to a housing 12 (e.g. a compressor shell), which defines an opening 14. The feed-through 10 includes a metal cap 16 having a bottom wall 18, a cylindrical sidewall 20 around the bottom wall 18, and an annular flange 22 extending from the cylindrical sidewall 20. The cylindrical sidewall 20 is disposed within the opening 14. The bottom wall 18 includes a plurality of apertures 24 through which a plurality of current-conducting pins 26 are disposed. A plurality of insulating seals 28 are disposed in the apertures 24 to seal the plurality of current-conducting pins 26 to the metal cap 16.
The feed-through 10 is installed to the housing 12 by resistance welding. Resistance welding refers to the joining of two or more pieces of metal by applying heat and pressure without the addition of any other material. Welding heat is generated when the parts to be welded, which are placed between two electrodes, resist the passage of electric current between the two electrodes, while pressure refines the grain structure in the parts. This combination of pressure and heat causes the parts to be welded to coalesce without actually liquefying. As clearly shown in FIG. 2, by using an upper electrode 30 and a lower electrode 32 to press the annular flange 22 against the housing 12 and by directing electric current through the electrodes 30 and 32, a weld 34 is formed at the contacting area between the housing 12 and the annular flange 22 so as to secure the feed-through 10 to the housing 12.
Installing the prior art feed-through 10 to the housing 12 by resistance welding creates the possibility that excessive heat may be generated which may migrate through the cylindrical sidewall 20 and the annular flange 22 to the insulating seals 28, particularly if the installer (e.g., the compressor manufacturer) does not exercise due care in handling and installing the feed-through. If excessive heat migrates to the insulating seals 28 during the welding process, there is a potential that the integrity of insulating seals 28 may be compromised and thereby become susceptible to leakage.
Moreover, the forces applied by the electrodes 30 and 32 to the typical feed-through are not aligned, causing a bending moment around the contacting area where the weld 34 is to be formed. The bending moment may tend to deform the annular flange 22 and change the welding location on the feed-through 10, making the positioning of the feed-through 10 relative to the housing 12 and thus the welding process more difficult.
Recent developments in hermetic power terminal feed-throughs, particularly those for use in refrigeration and air conditioning compressor applications, though substantially improving performance and providing more efficient operation, have required the compressor manufacturers to exercise greater care in handling and installing the feed-throughs during assembly. In particular, the compressor manufacturers' welding techniques, equipment selection (including welders and welding electrodes) and control settings, are especially critical for achieving proper installation of the feed-through.
Improper installation of the feed-through is to be avoided, since such practice can cause damage to the feed-through and undesirable feed-through failures. For example, welding with improper equipment or under improper control settings can result in making the feed-through more susceptible to heat shock, diminishing the robustness of the glass-to-metal seal due to the abrupt expansion and contraction of the metallic body, pins and/or insulating material. Therefore, there is a need for an electric power terminal feed-through which can be reliably and easily manufactured and installed.